Apparatus for filtering



Nov. 27 195i D. E. BENCH 2,575,275

APPARATUS FOR FILTERING Filed May 29, 1948 2 SHEETS-SHEET- 1 nAwn E. BENCH TLA@ fw ATTORNEYS Nov. 27 195! D. E. BENCH 2,576,275

` APPARATUS FOR 'FILTERING Filed May 29, 1948 2 SHEETS- SHEET 2 IN VEN TOR I DAVID E. BENCH j@ Bv Patented Nov. 27, A1951 UNITED V'STllifI-ES CFY'FIC'E 2,576,275 v' v APPEATsFoR' nfriI' Davia eenen, Dayton, ohiw-.assignor w'rie lCommonwealth Engineering Company of; Ohio;

Dayton, Ohio, a-corporation of Ohio Y Armies-amenities;194s;sisrfnaabeof2 f i claims: (o1. aid-litt 1 This-'invention relatesto?lteringdevices; and ini particularlto continuousf'and automatic lter'sa In' thevr arit*y of filtering' it-"liasv long` ben recoge n'izedL-that'an ideal-lt'ering system would besubcontinuously'v onf'automaticcycle for maintaining tion.-y Y Y Yet another-'bject'off' the: invention 'istlie prof-- stantiallycontinuousiand' automatic thereby re# 5' vis-ion; ii'r flteringapparatusof the characterv ducing to a minimum the down time'V of the'I equipment'wlfiile the' fluid is being ltered and also?'maintair'iingy the' conditions of l the-fluid'V in the' equipment-as nearly 'riform as possible at alltimesi Inr practieef most-'ltering'r devices' are of the batch-'type `Vaiii'd operate" intermittently either by olosirigfoia po'rti'on 'of' the filtering-'member durin'g the 'tiiiiethe surface:v thereof is" beingfreno#A va'te'df or by? replacing-'I it: With' another filtering member?.

Botti ofthese methodsfof operation' are unsatisfactory; because-iii:K the l firs'tl case vasubstantial' portion of the ltering member isrendered inactiveat all times,.\aiid in-the secondcase two filte'r'ingfmembers; usually inf the" form of drums; must be' provided` and i-naddition'f auxiliaryequipment, i such asfoverhea'd cranes and: the like;- must be-` 'available'i for liftingout' the used drum!Y andsinserting thenew. -v

In thef` applicantsIco-pendingl application; iri`v Whichhefwas izo-inventor with Albert (j). Fink, andfwhichis identified by. Serial No.--794,634, and filed December 30, 1947, there is shown a 'filteringv system which approahesacontinuous filtration process and Which obviates a great many of the shortcomings" iound in' iilterir'igx devices? of the p'rioiia'rtx.`

Theinstai'it afppliation af furtherri develope' meiitand extension--offcertain inventivefeatiire's'- o1A thl'aboy rentiofie'd appli'ctiomf Serialg No. 79431634 l andlhasfritslprincipal objeet'tlriefpro1V visiefif ofi as simple -aiid effective ilteriiig" system f which is substantially! continuously' in 1 opratio'n' Ai-stillfu'i'tlfierA obj ect oi the present'. invention isthe'L provision of a-ifiltering systenfiwhich will l simulate continuous -operating"l conditions and whichi'accomplisli'es th'is iresiiltfwith" a Arelatively simple-frechanismi It is''alsoan objectof 'f this-'invention i to"provide anfl improvedfiltering arrangement especially' adapted for'l'iisingib'rous 'lterlaid materials! Y Another' object of the invention is the provisionof filtering apparatuso'fthetypevaforesaid `in. Which 1 the" solution4 bein'gl4 ltered fis introduced intoia .'lteriiigitankf andaL filter aid is added tov th'eincoming solution so'i as to thoroughly? disperseithe ilterfaid.'y

It isfsalan objec't'f 'fthisIiriventionritoprovide fabove noted-,of a"bypassfarrangementwhich'may be utilizdfwhenthef solution'rbeing 'filtered een?" tains dirt solids-to return thesolution tdtlieffllter` tankbut vvhohlby-passfmay' b e-fcu't, out When't-he solutions being: handled'a're' clean to moderately iliii'ly?.v i

Still another objectE of the' inventior'i's' the"` provision, ltering apparatus?" in'cli'idin'gff..afy rotatable drum* and" sdrapingblade;A ofmeans for 1-5 introducing'filtered"solutionftogether with lterj 2g simulated. 'Moreoverva's the 'conoentre'jtion` of" dirt particles on the dium'isredce'd' the concen--f tration-off the'flter'aidisiinereased." e

These" and* otherv objects and A'advantages will' become more? apparent' fupor'rfreference'torthe "fol= lovving'f|` vdescription taken'iinlconnectin' with' the i accompanying drawingsirifwhich:

Figure? "2 is"- afdiagrainmatid wiring diagram* showin'gthe'eoiit'frl system forA eiectingftheautomatic/'control ofthefilteringJarrangeirient` shown in-'Fig-relfi Figure 3 is' fragmentaryfview' showinga' modi-f` fie'dfarrangement for." the'sciapingf blade4 which" removes ther surface--co'atingff-romY 'the filteringA drumv j t.

Figure 4 is a fragmentary view showing another". ara'ngem'ent" forv adding 'the'fbros Aiiltere'aid; rto

thelter'tankfandff' Y f Figurefr is-fa fragmentary vievvf` showing'one manner "off arrangngr'the' lter' forcontinuous" operation'rathenthan-'intermittenti operation:

:` Referring rtolr the drawings; thearrangement therein 'issubj ect :to contamination by' solids -dur- 3 from the bottom of the tank I to the top of the tank |4 and operates as an overflow so that fluid can be continuously passed from the tank I6 to the tank I4. Rotatably mounted in the tank I4 is a perforated drum I8. The drum I8 has its ends closed and is rotatably mounted on bracket means as shown at 26. A suction pipe 22 opens into the interior of the drum'fr' drawing fluid therefrom; A pump 24 in the conduit 22 draws a suction on the said drum and the fluid drawn from the drum in this manner is expelled under pressure through the conduit 26 to the tankv I0. In this manner fluid is continuously'circulated from the tank IIJ to the tank I4, then through .ther

.actually are very small, and one preferred form of shell for the drum I8 comprises a metallic member which is formed by an electrical process and which is foraminous by virtue of a plurality of very .tiny apertures therein of only a few thousandths of an inch inV diameter.V

Between the pump 24 and the tank I6 there is` a three-way valve `3l) which is normally urged-by a spring 32 into position to connect the discharge side of the pump 24 with the conduit 26. Upon energization of a solenoid SI .associated with the valve 30 the said valveV is shifted to connect the pump discharge with a conduit 34 leading toa head box 36 which is located somewhat above the upper level of the fluid in the tank I4. 'Ihis head box may have a partition 38 therein and a screened outlet chamber 40 which is connected by a conduit 42 with a manifold extending longitudinally along the drum I8.

Positioned above the head box 36 is a hopper 46 having a rotatable measuring discharge element 48 connected with adrive motor M2. When the motor M2 is energized .the measuring discharge element 48 .rotates and discharges material from the hopper 46 into the head box 36.

The material in the hopper 46 is filter-aid which, as is well known in the art, coats the surface of a ltering member through which fluid is being drawn and acts to. set up irregular small channels which permit the fluid being filtered to flow therethrough, but `whichretain the solids and gels being ltered from the fluid. In the particular example shown inthezdrawings the type of filter-aid is iibrous, but itwillfbe understood that granular filteraids,: such as the diatomaceous earth, could be employed if de-` sired. v

vBearing on the top of the drum'immediately forward of the manifold 44 is?;a scraping knife 50 whichis adapted for stripping the coating of lter aid from the surface of the drum I8 as the said drum is driven inrotation. The driving of the drum may be effected by the motor MI through the worm and wheel reduction gearing 52 as shown in Figure 1v and the direction of rotation of the drum is counterclockwise as viewed in Figure 1. l y

The control of thevalve 30 and the operation of the filter-aid dispensing mechanism above the head box 36 and the driving of the drum I8 by the motor MI is accomplished bythe electric circuit shown diagrammatically in Figure 2. In this figure there areethe power lines LI and L2 pi L 4 and therebetween is connected a timer marked T which is in series with the normally closed blade 54. The blade 54 is connected with a re-i silient expansible member 56, such as a bellows, and which in turn is connected by a conduit 58 with the inlet side of a valve 68 in the conduit 26 as shown in Figure l.

When the pump 24 is discharging above a predetermined rate the pressure established ahead of the valve 60 will be conveyed through the conduit 58 to the expansible bellows 56 and urge the blade 54 away from its associated contacts and thereby retain the timer T de-energized. However, when the flow rate vthrough the pump 24 falls below the said predetermined amount, the loss in pressure ahead of the valve 60 permits the bellows 56 to collapse and the blade 54 to close on its associated contacts, thereby energizing the timer T. 1

As is well known in connection with filters the rate of flow therethrough is a direct indication of the need for yrenovating the surface of thev filter, and whenever the said rate is below a predetermined amount it is desirable for a clean filtering surface to bepresented to the uid to be filtered.

The timer T has a first blade TI which bypasses the blade 54 and acts as a holding circuit for the said timer. The timer also has a blade T2 which is in series with a selector switch 62 and the solenoid SI associated with the valve 30. A third timer blade T3 is in series with the motor' MI and controls the driving of the drumV I8, a timer blade T4 is in series with selector switch 98 and the dispensing motor M2 which controls the supply of filter-aid to the head box 36,and' a fth blade T5 is in series with a selector switch 82 and a motor M3 for a dispenser to be described presently.

In a manner well known in the timer art, energization of T will immediately close blade TI which will thereafter remain closed until the time v period has elapsed. During this predetermined period, blades T2, T3, T4, and T5 will close and open according to whatever functions are controlled by them. The operation of these last named blades willbecome apparent from the following description of the operation of the filter.

Operation In outlining theoperation of the above dej scribed arrangement attention is rst called to the face that the apparatus is adapted to be used on solutions which are contaminated to varying degrees. Thus the solution might be clean to moderately dirty under which circumstances the arrangement of Figure 4 would be used in which the bypass 34 is eliminated. On the other hand the solution might contain dirt solids inA -which case the bypass 34 is employed. The latter arrangement is now described as follows:

Let it be assumed that the drum I8 is covered with a filter aid material and that the pump 24` Vis running and drawing fluid from the drum I8 and returning it through the conduit 26 to the tank I0. The control circuit of Figure 2 is pre#- pared by closing selector switches 62 and 90 and opening selector switch 92.

Let it now be assumed that the residue filtered from the liiuid so restricts the iiuid flow through the drum that the pressure ahead of the valve 60 drops to the point where the blade' 54 closes on its contacts. This will' energize the timer T, whereupon the blade TI thereof is closed to..

establish La holding. circuit; aand to energize the solenoid SI which will maintain the timer ener-i gized-for a predeterminedlperiod.- Energization of the ftimer also closes 1-2T2, `which fshifts the valve 30 to divert-the ypumpdischargeV through the conduit 34 andhead box 36 back to the filter.- ing tank... Y

This closed circulation ,..of the fluid through the filtering tank and drum continues,:and after a predeterminedtime substantially all of the foreign material inthe fluid. is filtered therefrom. Thereafter, and with the said circulation of fluid continuing the blade T3 closes and energizesthe motor MI and commences the drum Ill'torotat-` ing counterclockwise so that the scraper-blade 50 commencesA to scrape the surface f l-coating therefrom. This operation' may continueuntil the entire surface Aof the drum is completely clean. iPreferably the pump `2li ismaintained inoperation duringthistime in order to preventfilter aid and residue dislodgedfro'm the Asurface of Athe-drum by the action of the scraperblade from falling into tank l0 andproviding a source-of contamination for fluid 'subsequently passed there- "Assuming that vthe rotation vof the `drum'continues until it is scrapedclean,"then"the Vblade T3 Will open to de-energize'the motorlVll and halt rotation of the drum vand the`blade14 `will close to'energize the motoriM2 and to commence operation of the filter aid dispensing mechanism above the head box 36.

It will be' noted that, since vthe solution' isr circulating through druml andtank' i4 via the conduits 34 and 42 andh'ead' box 36', the` lter aid dispensed is introduced -into'a streamof the solutionv and, thus, "dispersion'of the filter vaid to a high degree `is assured,

,As the lter-'aid is so dispensed into the head box itis carried therethrough through the discharge Vchamber 40 and conduitl 42 to the manifold` 44 and expelled vinto the l'tertank. Thefllter-aid will be caught'on th'e'surfa'ce of the drum and" deposited Arelatively uniformly thereover.V Uniform deposition Yof the "lte'r aid on the drum obtainsbecause `ther-fluid'carryingI the filter aid always'low's vmostrapidly through that 'part ofthe 'drum surface/having the thinnest layer Yof iter cake thereon.- Afteralpredetermined amount' of :lter-aid hasbeen dispensed the timerblade VTl! Ywilliopen andhal-t Ythe dis pensing of filter-aidinto Ythe head box.` Dueto the kcirculation of -fluidthrough the headfbox, after a short `time all of the'lter-aid which -has been delivered to the head box willbe conveyed to the ltering tank and thereinedeposited on the drum i8. Thereafter the blade T-I opens to de-energize the timer, andthe recoating -1 cycle is completed. De-enerization of thetimer opens blade T2 thereof and'permits the valve 36-to return tothe position shown in- Figure 1 and where,-A in the discharge of the pump is directed' through the'conduit 26 to the'tank il); At this time the entire surface of the ldrum i3 is coatedlwith a drops the foregoing` cyclelof operations will again take place.

It will be evident that the operations described above need not be carried out consecutively as described, but that the dispensing of: lter aid material could take place concomitantly with the scraping of: the drum'. This, infact, is the pref ferred method .ofoperation, yand it will `beet/ident' tha-tl the slurry'of lteraid :material and uid discharged from the manifoldtM- will coatout on the drum. la immediately behind the scraper blade 5i), because that is the portion ofthe drum throughwhich iiuid is flowing at the maximum rate.

It will be. evidentthat the onlything that is necessary to adjust the system lfor one method'of operationor the other is adjustment of thel order of closingof the timer blades and the length of* time that they remain closed.

yIn .connection with the first mentioned method of operationwherein thedrum is entirely Ycleaned Yand then thenew filter cake built up thereon,;the filter aid material may be dispensed by the .arrangement shown: in Figure 4. and whereinthe bypass conduit `3.1i is entirely eliminated. -r

In Figure @the-,filter aid dispensing .hopper 46 is located over the tank I4 immediately'above the point where the conduit I6 opens into :the said tank. This is in the critical region where it is `.desired'to introduce the lter aid to .avoid fouling of the screen. A small head box arrangesY ment 64 having a screened outlet 56 is :provided for insuring that the filter aid material YWill `be properly broken up in the fluid before reaching the surface of the `drum I8. The :dispenser in Figure 4 is operated by; a motor M3, as shown.

In the arrangement .of `Figure 4 it will be noted the filter aid is introduced the stream of the incoming solution immediatelyv the latter leaves the conduit I6. This follows the same plan hereinbefore discussed for providing for gooddisfpersion of the filter aid. f

When :the arrangement shown in'Figure 4 is utilized, the selector switch 62 is moved to its open position to prevent operation of the solenoid Si. The selector switch 96. is moved to its open position to prevent operation of the dispensing motor M2, and the selec-tor switch 92 is moved to its closed position so that upon operation of the timer blade T5, the dispenser motor M3'Wil1 operate.

When it is desired to renovate the filter cake on the drum in the arrangement shown in Figure 4, it is merely necessary to set the drum to rotating and simultaneously to dispense iilter-v-aid material into the head box 64 by energizing the motor M3. The direction of rotation ofthe drum isfas before, counterclockwise. After thedrum has made 'one"revo1utionj, rotation thereof is halted, Whileoperation of the dispenser may continue for a short period of'time if desired.

Duej to the fact that the highest rate of fluid fiowthrough the drum Will take place'overthe portion thereof having the thinnest ,filterv cake, the foregoing described method of suppiyingcake forming material to the surface of the drum will result in a relatively uniform deposit of lter cake having good filtering characteristics. Optionally, the Figure 4 arrangement may be operated so that one complete revolution of the drum takes place before action of the dispenser is initiated. The exact manner of operating' the arrangement shown in Figure 4, or any of the other arrangements, wil depend on the particular nature of the filtering cycle being carried out and whether 'or not the requirements are sufficiently rigid to require batch type operation or continuous operation.

MA feature common to all .of the methods .of operation described above resides in thearrangef mentV for dispersing the cake forming filter aid material into the stream of fluid flowing toward the filtering drum. In practice it has been found that the material can be thrown into the filtering tankloosely and at random, and it will stillnd its way tothe surface of the drum and coat it uniformly, due to the fluid flow from the tank into the drum. However, in order to avoid any'concentration of dirt. on the surface of .the

drum'which might clog the fine openings therein, it. is preferred to introduce the cake forming material'into the stream. of fluid entering the filtering tank, whereby Athe dirt in the iiuid is admixed with and entrained in the filter aid and is', therefore, removed from the drum whenever the lter cake is scraped therefrom.

.In .connection `with the useof fibrous filter-aid material, `it has been found desirable to bring about relative circumferential movement between the scraper blade and the peripheral surface of the filtering drum. This relative movement is oscillatory in nature and is in addition to the relative movement of the drum and blade during removal of the cake` from the drum and superimposed thereon. It has been found beneficial because fibrous filter aid material includes fine laments, the ends of which enter the holes in the periphery of the drum and tend to hold the lter cake on the drum so a simple scraping action is not suiiicient completely to remove the cake. By the oscillatory or vibratory movement of the blade, as in Figure 3, acake of brous material can be completely removed from the drum. One manner of accomplishing this is shown in Figure 3 wherein the scraping blade comprises a relatively thin blade 68 and which is mounted for oscillatory movement in the guide means 10. A

draglink 'I2 connects the blade with a rocking arm 'I4 which is pivoted on the edge of the tank I4 and which has one end connected with a motor driven eccentric '16. In operation, the motor driving theeccentric 'IB is preferably connected in parallel with the drum driving motor MI and operates during the same period of time.

The arrangement shown in Figure 5 is one manner of obtaining continuous operation of the lter. In this figure the filter drum I8 is connected through a speed changing unit 'I8 with the drum driving motor MI. The gear reduction unit is connected with a ratio changing motor 8l) so that in one direction of rotation of the motor 3U the unit I8 is adjusted so that the drum I8 rotates more rapidly and in its other direction the unit 'I8 is adjusted so that the drum I8 rotatesmore slowly. The direction of operation or" the motor 80 is determined by the switch 82 `which may be controlled by the bellows 84 which is connected similarly to the bellows 5B in Figure 2.

When the bellows expands Vbeyond a predetermined point indicating flow above a certain rate through the filter drum, the motor 80 is adjusted to reduce the speed of the filter drum. When the bellows 84 collapses, thereby indicating a reduction in fluid flow beyond a predetermined level, the motor 8) rotates to adjust the unit 18 to increase the speed. In this manner the drum I8 is caused to rotate at the optimum Vspeed maintainingthev filtering rate therethrough at a desirable high level, but maintaining the speed of rotation at a sufficiently low level that the unit economical in its use of lter-aid material. The dispensing of lter-aid material is correlated with the speed of operation of the drum by the flexible drive 86 extending from the drum driving 8 shaft t0 the filter-aid dispensing mechanism at It will4 be understood .that this invention is susceptible to modification in order to adapt it to differentusuages andeonditions and, `accordingly, it is desired to comprehend such modifications within this invention as may fall within the scope ofthe appended claims.

I claim:

..1. In a lter; a tank, a drum having a perforate periphery in the tank entirely below the normal liquid level of the tank, pump means having its inlet connected with the interior of the drum, a scraper blade bearing on the surface of the drum to remove the entire thickness of the filter cake thereon upon rotation of the drum, a motor for driving said drulm,rmea-ns responsive to a predetermined reducedlflow rate through said filter for initiating energization of said motor, and timing means for maintaining said motor energized until the drum has made atleast one complete revolution.

, 2, In a filter; a tank, a drum having a perforate periphery in the tank entirely below the normal liquid level of the tank, pump means having its inlet connected with the interior of the drum, a scraper blade bearing on the'surface of the drum to remove the entire thickness of the lter cake thereon upon rotation of the drum, dispensing means for supplying a measured amount of cakeforming material to the tank externally of the drum, a motor for driving said drum, means operable in response to a predetermined reduced flow rate through said iilter for energizing said motor to commence rotarymovement of the drum, means for main-l taining said motor energized until the drum has made at least one complete revolution, and means for actuating said dispensing means during energization of said motor.

3. In a filter having a tank, a drum having a perforate periphery in the tank entirely below the normal liquid level thereof, a scraper blade bearing on the periphery of the drum so rotation of the drum will cause removal of the entire thickness of a lter cake therefrom, a dispenser for dispensing measured charges of cake forming material to the tank externally of the drum, motor means for driving the drum and dispenser, speed varying means for said drum, means responsive to a predetermined reduced rate of ow of fluid through said lter for initiating energi'zation of said motor means, and other means controlled by the flow through the lter forsaid speed varying means.

4. In a filter; a tank, a drum having a perforate periphery in the tank below the normal liquid level thereof, a pump having its inlet connected to the interior of the drum, a scraper blade bearing on the surface of the drum, a dispenser for dispensing measured charges of filteraid to said tank externally of the drum, time controlled means responsive to a predetermined reduced flow rate from said pump to initiate rotation of said drum and to initiate operation of said dispenser in timed relation whereby said blade scrapes material from said drum surface and said dispenser discharges material thereto, and means for maintaining said drum in motion for one complete revolution after being started regardless of variations in said fluid flow.

A 5. In a filter; a tank, a drum having a perforate periphery inthe tank entirely below the normal liquid level thereof, a scraper bearing on last named means including means for Lcontrolling the speed of said driving means whereby the rate of rotation of the drum and the rate of dispensing by said dispenser are adjusted in accordance with the rate of said fluid flow.

6. in a filter; a tank, a drum having a perforate periphery in the tank entirely below the normal liquid level thereof, a scraper bearing on the surface of the drum, a pump having its inlet connected to the interior of the drum, a dispenser for dispensing measured charges of cake forming material to the inuent side of the drum, driving means for driving said drum and dispenser, and time controlled means responsive to the rate of ilow of iiuid being ltered through said filter for operating said driving means in timed relation, said control means including means for controlling the speedrof said driving means whereby the rate of rotation of the drum and the rate of dispensing by said dispenser are substantially inversely proportional to the rate of said uid ow, and means for oscillating said scraper blade during rotation of said drum.

7. In a filter; a tank, a drum rotatably suspended in the tank entirely below the normal liquid level thereof and having a perforate peg riphery, a pump having its inlet connected with the interior of the drum, a scraper blade bearing on the periphery of the drum, a normally closed bypass line opening from the discharge side of the pump into the tank, a head box in said bypass line above the normal liquid level of the tank, a dispenser operable to dispense cake forming material to said head box, a manifold opening from said head box to a position behind the scraper blade, and control means automatically responsive to a predetermined reduced rate of flow of fluid from said pump for opening said bypass line, said means including time controlled means operable after said line is opened for causing said drum to rotate and for initiating operation of said dispenser in timed relation.

8. In a filter; a tank, a drum rotatably suspended in the tank entirely below the normal liquid level thereof and having a perforate periphery, a pump having its inlet connected with the interior of the drum, a normally closed bypass line opening from the discharge side of the pump into the tank, a head box in said bypass line above the normal liquid level of the tank, a dispenser operable to dispense cake forming material to said head box, a manifold opening from said head box to a position behind the scraper blade, means for rotating said drum and operating said dispenser, and control means automatically responsive to a predetermined reduced now rate of fluid from said pump for opening said bypass line, rotating said drum and operating said dispenser, said control means including, time delay means whereby rotation of said drum and operation oi said dispenser occurs after said line is opened, and said control means including means finally operable after a predetermined greater time delay to halt said drum and to stop operation of said dispenser and to close said bypass line.

9. In a lter having an inlet normally receiving contaminated fluid from a work station and an'outlet normally discharging filtered fluid to the work station, a member between said inlet and outlet for supporting a iilter cake, scraping means bearing on said member, a dispenser actuatable for dispensing cake forming material to the inlet side of said member, motor means energizable for moving said member, normally ineffective bypass means for diverting the entire discharge of said lter from the outlet thereof to the inlet for closed circulation of fluid through the filter, flow responsive means arranged to be sensitive to the discharge rate of said filter, and control means controlled by said flow responsive means and actuated thereby whenever the rate of discharge of said filter reaches a predetermined low value to make said bypass means effective, said control means including means operable a predetermined time after said bypass means becomes effective to energize said motor means and to bring about actuation of said dispenser, and after a predetermined greater time to again make said bypass ineffective.

10. In a filter; a tank, a drum therein, a suction connection to the inside of said drum, a scraper on said tank bearing on the periphery of said drum, a dispenser for dispensing cake forming material to the tank outside said drum, a rst motor energizable for driving said drum whereby said scraper will remove the cake from the drum, a second motor energizable for actuating said dispenser, control means normally maintaining said motors deenergized and operable when actuated to energize said motors, and flow responsive means arranged to be sensitive to the rate of fluid flow through said lter for actuating said control means when the said rate reaches a predetermined low value, said control means including timing means for maintaining said motors energized for a predetermined period.

` DAVID E. BENCH.

REFERENCES CITED The following references are of record in the n file of this patent:

UNITED STATES PATENTS Number Name Date 1,515,130 Morrison Nov. 11, 1924 1,579,171 Zoul Mar. 30, 1926 1,619,042 Sauer Mar. 1, 1927 2,020,693 Manley et al Nov. 12, 1935 2,055,869 Manning Sept. 29, 1936 2,102,780 Bielfeldt Dec. 21, 1937 2,270,938 Doescher Jan. 27, 1942 2,300,908 Broughton Nov. 3, 1942 2,301,430 Malanowski Nov. 10, 1942 

